We will study three peptidases that cleave biologically active peptides. We will purify kininase I or carboxypeptidase N, the inactivator of bradykinin and anaphylatoxins. We will separate the active subunits of the enzyme, study their substrate specificity, their immunological identity, and the mode of cleavage of the macroenzyme to active subunits by plasma proteases - the inhibition of kininase II or angiotensin I converting enzyme from the kidney and from the gastrointestinal tract will be studied with model inhibitors. The effect of inhibition on function of converting enzyme bound to plasma membrane will also be established - finally, attempts will be made to characterize with model substrates and the site of cleavage of the active peptides will be determined.